How can I reference a outside variable from within a function?

Question

UPDATE: Sorry I was wrong with my assumption of the problem. Its due to me trying to make the function parallel and have multiple proceses change the same dictionary. How can I design my function so it allows for this? If I have to send the dictionary(in this case) then it'll keep overwriting itself and can't span over all the cores. I'm happy to redesign the function but not sure how i can do it and still spread it over multiple cores.

To simplify, I basically have something like the following:

list = [1,2,3,10]
dictionary = {}
for x in list:
 for xx in range(100):
 for xxx in range(100):
 dictionary[x]=xx*xxx

This works, but when I wrap the for loop in a function, I get: NameError: global name 'dictionary' is not defined

def test(x):
 for xx in range(100):
 for xxx in range(100):
 dictionary[x]=xx*xxx

I know this has something to do with the namespace but I don't want to send variables to the function in this case because I think it'll overwrite the variable dictionary. How can I reference the dictionary variable while in the function? The reason I ask is I want to create a process that spans multiple cpu's, so I don't want to declare the variables in each function.

I'm using functions but if I need to use classes or there's another way to get around this then please me know and I'll rethink my approach.

Answer 1

Try again:

lst = [1,2,3,10]
dictionary = {}
def test(x):
 for xx in range(100):
 for xxx in range(100):
 dictionary[x]=xx*xxx
for x in lst:
 test(x) 

You only get a NameError when a name is not defined. It has nothing to do with scopes.

• Lostsoul: ahh your right..I tried it on its own and it worked. I was trying to take a proces I had and wrap it into the above function so I can use the pp module to have multiple cpus work on it. Seems to happen when I'm creating jobs using it.

Answer 2

How can I reference a outside variable from within a function?

Don't. Pass it as a parameter.

• Lostsoul: but i want to avoid having to pass a ton of reference variables
• Karl Knechtel: Why exactly are you expecting to need "a ton" of them? Maybe your function needs redesign.
• Lostsoul: For example, say I have a function and a counter to count the number of times its successful. If I distributed the job over multiple cpus, then sending it to each function would restart the counter each time a new process is created.
• Caleb Hattingh: @Lostsoul: then put your data into a dict and pass that in, then unpack them inside your function. References to global variables are generally a bad thing.

Answer 3

Try to avoid global variables and pass the variables needed into the function:

>>> def test(x, dictionary):
... for xx in range(100):
... for xxx in range(100):
... dictionary[x] = xx * xxx
... 
>>> list_of_numbers = [1, 2, 3, 10]
>>> dictionary = {}
>>> 
>>> for x in list_of_numbers:
... test(x, dictionary)
... 
>>> print dictionary
{1: 9801, 2: 9801, 3: 9801, 10: 9801}

I've renamed list, since it is a Python built-in.

This can clearly be simplified to:

>>> for x in list_of_numbers:
... dictionary[x] = 99 * 99